1. Field of the Invention
The present invention relates to hand-held powered chain saws. More particularly, the present invention relates to a safety brake mechanism for such chain saws.
Portable chain saws of the type here under consideration are utilized by an operator grasping the apparatus with both hands. These chain saws are provided with what may be termed a control handle extending generally rearwardly of the saw housing. Another handle, which may be called a frame handle, is usually disposed transversely of the saw adjacent the forward portion thereof. A throttle for the gasoline engine of the saw is mounted adjacent one of these handles.
During a cutting operation, the cutting chain may often engage a green limb, for example, at the tip of the guide bar thereby causing an abrupt movement of the chain saw. This condition is commonly referred to as "kickback." This abrupt action of the chain saw may cause the moving cutting chain to come into contact with the head, face or other parts of the operator's body thereby resulting in serious injury or even death.
2. The Prior Art
The prior art includes various safety devices for preventing, or at least minimizing the possibility of, injury to the operator by a chain saw as a result of kickback or other operations wherein the moving cutting chain could be brought into contact with the operator's body. Generally, these devices include guard members moveably mounted adjacent the frame handle. Should the chain saw rotate rapidly as a result of "kickback," the guard member will usually come into contact with the operator's wrist or the back of his hand thereby actuating a brake to arrest movement of the cutting chain. These guard members may be provided with sufficient mass such that the brake will also be activated by inertia in response to a sudden movement of the saw, such as in the case of kickback. Representative prior art U.S. patents showing such devices include: Mattson et al., No. 3,664,390; Moore, No. 3,739,475; Gustafsson, No. 3,776,331; Moore, No. 3,793,727; and Dooley, No. 3,839,795.
These prior art devices, although generally satisfactory, suffer from two principal deficiencies. First, the safety brake mechanisms shown in these patents are rather complicated thereby contributing significantly to the weight of the chain saw. Needless to say, it is important that hand-held chain saws of the type here under consideration be as light as possible to facilitate their ready handling, particularly in the case of tree trimming. The second deficiency of these prior art devices is the somewhat high cost of these brake structures resulting from their complicated nature.